Q: How do I insert a slideshow into a post or page?
A: Upload your photos to the post or page using the media uploader. The media uploader also allows you to assign titles and captions, sort, and delete photos. Then add the shortcode [portfolio_slideshow] where you want the slideshow to appear in the page. See screenshots 2 and 3 for an example. Here's a video of how to upload images in WordPress 3.5.
One common mistake is to insert the images into the post using the content editor. This is not necessary--the plugin detects all images attached to the post and creates the slideshow automatically.
Q: Does the plugin support images that are not uploaded via the media uploader?
A: No, the plugin does not support random folders of images or images on a third-party site. All images must be uploaded using the media uploader, which creates the database entries the plugin relies on to generate the slideshow. This behavior will not change in future versions of the plugin.
Q: Why isn't my slideshow loading?
Try disabling other plugins and switching to the default theme and see if that fixes the problem. You may need to get in touch with the author of that plugin to make sure they are loading jQuery correctly.
One other problem that I've seen is the missing "cycle" plugin. View your source to see if "jquery.cycle.all.min.js" is being loaded. If not, make sure your theme has the line in footer.php, which is where the cycle script is loaded. All themes should have this line, but every once in a while it goes missing.
Q: How do I change the size of the images?
A: By default, the slideshow uses the large-size images that are generated by WordPress when you upload an image. You can change this default in the settings panel for the plugin, or on a per-page basis using the size attribute (see installation instructions for usage).
If you would like to change the size of the images system-wide (for example, you want a large image to be 800px instead of 1025px) you can change the WordPress settings in the "Settings -> Media" control panel. You will need to regenerate your thumbnails to make the setting retroactive.